ND Exposure

Metered the scene, then screwed on a 10-stop filter and lost the shot to mental arithmetic? ND Exposure turns your metered shutter speed and the filters you stacked into the new exposure time, then counts it down for you.

HOW IT WORKS

Set the shutter speed your camera metered before the filter went on. Tap the ND filters you are using — tap more than one to stack them. The new exposure time appears immediately, as a fraction for short exposures and as minutes and seconds for long ones. Start the timer and shoot.

WHAT YOU GET

- New exposure time from your metered speed and total stops

- Filter stacking, with stops added correctly instead of multiplied

- A countdown timer for the exposure, so you are not watching a phone clock

- The screen stays awake while the timer runs, then releases

- Custom stop entry for filters and variable NDs that are not in the preset list

- Light reduction factor shown alongside the stop count

- Save up to 10 recent calculations and reload any of them

- Works without an internet connection for the calculation and the timer

STACKING ADDS STOPS

Put a 10-stop and an 8-stop filter together and you have 18 stops, not 80. Stops are exponents, so they add — the light reduction factors are what multiply. Tap both filters and the app does this for you, and shows the resulting factor so the arithmetic is visible rather than hidden.

FILTER NAMES, NOT ROUNDED LOGARITHMS

Filters are labelled the way the industry labels them. An ND1000 is treated as 10 stops, because that is what it is sold and used as, even though 1000 is not exactly 2 to the 10th. The numbers here line up with the markings on the front of your filter.

THE TIMER KEEPS REAL TIME

The countdown runs on elapsed real time, so locking the screen or switching apps mid-exposure does not stall it. Come back and the remaining time is already correct. Long exposures are where a timer that drifts is worse than no timer at all.

BUILT FOR

- Landscape and seascape photographers smoothing water and cloud

- Architecture shooters clearing people out of a frame with a long exposure

- Anyone working with a 6-stop, 10-stop or 15-stop filter where the math stops being intuitive

- Photographers learning how stops, shutter speed and density relate

NOTES ON SCOPE

This app calculates exposure time and times it. It does not connect to or control your camera, and it does not fire the shutter — set your camera to bulb or to the calculated time yourself. Strong ND filters can shift colour and lose a little more light than their rating suggests, so treat the result as a starting exposure and check your histogram.